The present invention relates to electrical filters and more particularly to stopband (notch) and passband filters having controlled gain and low ripple.
The synthesis of wideband filters with controlled amplitude characteristics within a stopband or passband is a difficult design problem. The synthesis of such stopband and passband filters is further complicated in most circumstances because insertion losses must be kept low to prevent deterioration in the noise figure for receivers or wasted power output for transmitters. Also, 1:1 input VSWR is required to prevent reflected power from degrading the system performance within both the pass and stopbands of the filter. Filter networks exhibiting controlled amplitude characteristics have been constructed by using active devices to combine signals in prescribed manners. However, the performance of such networks is not acceptable for many applications because of their complexity, inherent intermodulation and harmonic distortion and because they require DC power sources.
It is therefore an object of the present invention to provide a filter system which may be configured either as a stopband (notch) or passband filter and which exhibits controlled amplitude characteristics such as prescribed gain and low ripple throughout the stopband or passband as the case may be.
It is another object of the present invention to provide a filter system which is a stand-alone device not requiring DC power sources and which has 1:1 input VSWR and low insertion losses.
It is a further object of the present invention to provide a filter system which is easy to realize with real world component values, uses standard filter synthesis techniques to provide the required filter elements and otherwise uses components which are readily available at reasonable cost.